Unintentional ground detection for glass melting furnace provided with electric heating



United States Patent G UNINTENTIONAL GROUND DETECTION FOR GLASS MELTING FURNACE PROVIDED WITH ELECTRIC HEATING Herbert M. Augsburger, Toledo, Ohio, assignor to Owens- Illinois Glass Company, a corporation of Ohio Filed Apr. '12, 1957, Ser. No. 652,575

9 Claims. (Cl. 340--255) This invention relates to glass melting furnaces wherein heat is applied to the glass by Joule effect of electric currents passed between electrodes therein, and more particularly to method and apparatus for detection of unintentional electrical grounds occurring in the operating zones of the furnace prior to working.

Glass manufacturing furnaces have utilized Joule effect heating either as a sole source of heat for melting raw materials or in conjunction with heat produced by combustion of consumable fuels. The conventional furnace is generally constructed to have a melting zone wherein raw glass batch is introduced at one end or laid as a blanket over the top of the glass being melted therein. From the melting zone, the melted glass is passed through a throat passage to a refining zone Where it is fined. The fined glass is then withdrawn and fed into one or more working zones for conditioning and feeding to forming machinery.

It is desirable to have one or more intentionally grounded electrodes in the refining zone to prevent any electric potential to ground appearing on the glass being fed at the working zone.

If unintentional grounds occur at any of the energized electrodes of the melter, a current flow from the thus grounded electrode to an intentionally grounded electrode in the refiner will result. This current will, by necessity, pass through the throat passage from the melter to the refiner. Since the throat passage is a constricted channel, it becomes the most vulnerable part of the glass melting furnace to receive damage from uncontrolled currents flowing through an unintentional ground occurring therein. Obviously, unintentional grounds at other points in the furnace are objectionable, in that they result in the misuse of power.

Accordingly, it is an object of the present invention to provide a method and apparatus for detecting unintentional grounds in the melter or throat passage from the melter to the refiner by intentionally grounding currents in the glass at opposed ends of the furnace and comprising these currents to detect an unintentional electric ground occurring at other points in the furnace.

Another object of the invention is to provide current limiting impedors of predetermined impedance connected in series wtih the opposed pair of electrodes across the end of the melting zone of the furnace opposite the throat passage to make an intentional ground connection in the glass at a midpoint between said electrodes.

Another object of the invention is to provide an electrically responsive signal device triggered by a variation in the ground currents over the comparison of the intentionally grounded currents.

The specific nature of this invention, as well as other objects and advantages thereof, will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the annexed sheet of drawings on which, by way of preferred example only is illustrated one embodiment of this invention.

The figure is a plan view of a glass melting furnace 2,984,829 Patented May 16, 1961 provided with energized electrodes for applying heat to the glass in the melting zone of the furnace, and includes a schematic wiring diagram for the electric components utilized by the invention.

Generally the invention consists of applying a current limited ground circuit between the electrode or electrodes nearest the end of the furnace where charging would normally occur and comparing the current flowing through this ground with the current flowing through a ground connection from an electrode at the opposite longitudinal end of the furnace located in the refining zone. Normally with no grounds on the furnace, other than those intentionally applied as aforesaid, the magnitude of one of the grounded currents being determined by current limiting resistors or reactors; if an unintentional ground occurs at a point between the intentionally grounded points, the change in current in either of the grounded circuits will be detected by a device for comparing the current flow through the grounded circuit. Any change in this compared current flow may be used to electrically actuate an alarm system to warn of the existance of the unintentional ground at the instant it occurs.

In the figure, a conventional glass furnace is referred to generally at 10, and is comprised of a melting zone 11 and refining zone 12 which are respectively interconnected through throat passage '13. Working zones of the furnace, represented partially at fore hearths 14, are connected to receive glass from refining zone 12 for feeding and conditioning, as mentioned herein.

One pair of opposed electrodes 15a and 161; are inserted through the side walls of melting zone 11. A second pair of opposed electrodes 16a and 15b are inserted through the side walls of melting zone 11 nearer the throat outlet end thereof. Electrodes 15a and 1511 are electrically connected across one phase of a twophase transformed source.

In the energizing power circuit for electrodes 15a, 15b, 16a and 16b, the primary windings 17 and 18, representing separate phases of the transformer 40, are connected across lines 19, 20 and 21 of the two-phase, three-Wire supply. Electrode 15a is connected to secondary winding 22 on that phase of transformer 40 by lead wire 23 and electrode 15b is similarly connected by lead wire 24. Electrode 16a is connected at secondary winding 26 by lead wire 25, representing the other power phase of transformer 40, and electrode 16b is connected at secondary winding 26 by lead wire 27.

The glass near the batch charging end of melting zone 11 is electrically connected to ground as follows. Electrodes 15a and 16b are connected by wires 28 and 29, respectively, in series with iinpedors 30 and 31. The first ground line 32 is connected from the midpoint of the series circuit just described to ground. At the opposite longitudinal end of the furnace, grounding electrode 33 is inserted through the wall of the furnace in refining zone 12 and connected to ground through second ground line 34.

Through the connection of impedors 30 and 31 in series with electrodes 15a and 16b, a ground is effected in the glass in melting zone 11 represented at point A. An electric potential will appear in the glass at point A, and through reactors 30 and 31 the magnitude of current flowing to ground through ground line 32 will be of predetermined amount. Since an electric potential will also appear in the glass between electrodes 16a and 15b in melting zone 11, represented at point B, current will fiow through throat passage 13 from point B to electrode 33 and then to ground through line 34 returning through ground to line 32, 30 and 31 to point A. The magnitude of the current flowing through lines 32 and 34 to ground will remain constant so long as no other ground connections appear in the furnace. If, however, an unintentional ground does appear, such as for example in the walls of throat passage 13, the current flow in line 34 will be diminished in comparison to current flow in line 32, since part of the current from point B will be diverted to this unintentionally grounded point.

This occurrence is determined by electrically connecting either a differential or current balance relay 37 across a circuit comprised of a transformer 35 wound on line 32 and a transformer 36 wound on line 34. The relay 37 is set to retain its circuit open when these predetermined balanced amounts of current flow through lines 32 and existing when only intentional grounds are present. However, if an unbalance between the compared currents in lines 32 and 34 exists due to an unintentional ground oc curring elsewhere in the furnace, relay 37 in comparing the magnitude of currents flowing to ground in lines 32 and 34- will be actuated to close its circuit to connect a visual or audible alarm system warning of the existance of an unintentional ground in the furnace.

Relay 37 has an electrically responsive contact 14-4) to open and close a circuit to be presently described. This circuit consists of primary winding 41 of transformer 42 connected across one phase of electric main line supply, such as lines 20 and 21. One side of secondary windings 43 of transformer 42 is connected to one side of contact 140 by wire 44. The other side of secondary windings 43 of transformer 42 is connected to the opposite side of contact 149 by wire 45. An electric signal device 46 is connected into the circuit in series with wire 45. Electric signal device 46 may be either an illuminating light or a bell. The light will emit a visual signal when contact 144) closes the circuit (4d43d5) or the bell will emit an audible signal when contact 144 closes circuit (444345). Thus, whenever relay 37 detects through transformers 35 and 36 a current flow in lines 32 and 34 which varies from the intentionally impressed current flow, its contact 144 will close and give an alarm signal to notify of the existance of an unintentional ground.

Modifications may be resorted to within the spirit and scope of the appended claims.

I claim:

1. Ground detection apparatus for detecting intentional grounds in a glass melting furnace wherein heat is applied to the glass by Joule effect of an electric current passed therethrough between a source of electrical power and electrically connected electrodes comprising, a first ground circuit connected electrically to the glass body at one end of the furnace, said first circuit including in series the primary windings of a first transforme a second ground circuit connected electrically to the glass body at the opposite end of the furnace, said second circuit including in series the primary windings of a second transformer. means for causing an intentional current flow of predetermined amount from the glass body through each of said first and second ground circuits, a current comparison relay connected respectively across the secondary windings of each of said first and second transformers, and an electrically responsive signal means connected to said current comparison relay for actuation to provide an alarm signal whenever the said compared current flow in said secondary windings of said first and second transformers varies from said predetermined amounts of current flow.

2. The ground detection apparatus defined in claim 1, wherein said first grounding circuit includes an electric connection in series between opposed pairs of electrodes at the one end of the furnace through a predetermined amount of current limiting impedance to intentionally ground a current of predetermined magnitude flowing in said circuit.

3. The ground detection apparatus defined in claim 1, wherein said electrically responsive signal device emits a visual signal Whenever the current flow in said first or second ground circuits varies from the predetermined d quantity of current intentionally impressed to flow therethrough.

4. The ground detection apparatus defined in claim 1, wherein said electrically responsive signal device emits an audible signal whenever the current flow in said first or second ground circuits varies from the predetermined quantity of current intentionally impressed to flow therethrough.

5. Ground detection apparatus for detecting intentional grounds in a glass melting furnace wherein heat is applied to the glass by Joule efiect of an electric current passed therethrough between a source of electrical power and electrically connected electrodes comprising, a first ground circuit connected electrically to the glass body at one end of the furnace, a second ground circuit connected electrially to the glass body at the opposite end of the furnace, means for causing an intentional current flow of predetermined amount from the glass body through each of said first and second ground circuits, a current comparison relay, means for electrically connecting said current comparison relay to each of said first and second ground circuits to cause a current flow in said relay corresponding to current flow through said first and second grounded circuits, and an electrically responsive signal means connected through said relay for actuation to provide an alarm signal whenever the said compared current flow in said relay varies from the current flow therein caused by said predetermined amounts of said first and second intentionally grounded currents.

6. In a glass melting furnace having melting and refining zones, said melting zone provided with batch feeding mechanism at one end and a submerged throat passage connected to said refining zone at the opposite end of said melting zone, and electrode heating means for heating glass by Joule effect of electric current passed through the glass between electrodes in said melting zone, the combination therewith of: first ground means for intentionally electrically grounding current flowing in the glass contained in the melter from a point substantially at the midpoint of the batch feeding end of the melting zone, second grounding means for electrically grounding current flowing in the glass contained in said refining zone opposite the entrance of said submerged throat passage in said refining zone, means for controllin the normal amount of current flowing to each said first and second ground means during operation of said electrode heating means when no unintentional grounds in the furnace are present, and means for comparing the current flowing, respectively, to each of said first and second grounding means to detect any unintentional grounds occurring in the furnace.

7. Apparatus for detecting unintentional grounds in a glass melting furnace having melting and fining compartments and a passage interconnecting said compartments and wherein heat is applied to the glass in the melting compartment by Joule effect of an electric current passed through the glass in paths extending between spaced apart energized electrodes therein comprising means for normally impressing a first electric current of predetermined magnitude from current flowing through the glass in one longitudinal end portion of the furnace to an intentional ground connection, means for normally impressing a second electric current of predetermined magnitude from current flowing through the glass in the opposite longitudinal end portion of the furnace to a separate intentional ground connection, and an electrically responsive device connected electrically for comparing the said currents flowing to each of said intentional ground connections, said device being rendered unresponsive when said compared currents are of a ratio equal to the established ratio between their predetermined intentionally impressed magnitudes and said device being rendered responsive to indicate an unintentional ground present in said furnace when the ratio of 5. Said compared currents varies from the said established ratio thereof.

8. Apparatus defined in claim 7, characterized by including therewith an electrically actuated alarm device connected to be energized under control of said electrically responsive device whenever said latter device is rendered responsive by the presence of an unintentional ground in said furnace.

9. Apparatus for detecting unintentional grounds in a glass melting furnace wherein heat is applied to the glass by Joule effect of an electric current passed therethrough between energized electrodes therein comprising means for normally impressing a first electric current of predetermined magnitude from current present in the glass in one longitudinal end of the furnace to an intentional ground connection, means for normally impressing a second electric current of predetermined magnitude from current present in the glass in the opposite longitudinal end of the furnace to an intentional ground connection, and an electrically responsive device adapted to measure the ratio of the said currents flowing to each said ground connection, said device being rendered responsive only upon measurement of a ratio between said currents that differs from the ratio between the intentionally impressed currents, whereby said device, when rendered responsive, is operated to indicate an unintentional ground present in the furnace.

Wadman Apr. 30, 1935 Kennedy Apr. 29, 1958 

